There is a need for a system and method whereby large numbers of materials, and combinations of materials, may be rapidly and accurately scanned so as to determine their performance as components of electrochemical devices such as fuel cells, batteries, chemical reactors, catalytic systems and the like. Various systems for such high throughput scanning have been shown and suggested in the prior art. For example, the use of a combinatorial approach to study electrochemistry was first reported by Reddington et al., Ref. Science, 280, 1735 (1998). As disclosed, an array of material spots disposed on a large, flat working electrode of an electrochemical cell was prepared. As shown therein, an optical screening method was used to determine proton concentration within small active portions of the array. Such optical scanning methods are inherently limited because the variation of proton concentration is not easily detectable within the small areas of material spots in concentrated base and acid electrolytes. Other such combinatorial mass screening systems are known in the art. In one approach, a large container is employed to encompass a counter electrode, a reference electrode, and an array of material samples disposed upon multiple working electrodes. Such systems are shown, for example, in U.S. Pat. Nos. 6,187,164; 6,756,109; 6,818,110; and 6,132,971. In other similar systems, the multiplicity of materials being tested are disposed on a single working electrode, and such a system is shown in U.S. Pat. No. 6,913,849. In another approach of the prior art, a number of small containers are used to provide an array of electrochemical cells disposed upon a single flat base. Multiple electric leads are printed on the base and disposed to conduct electricity from each test sample to an analyzer. Such a system is shown in U.S. Pat. No. 6,758,951. In yet another type of system as embodied in U.S. Pat. No. 6,692,856, an array of sensor electrodes are inserted into a number of separate holes in an anode base configured to hold individual sensor electrodes. Further portions of the disclosed apparatus include a common counter electrode and a polymer membrane disposed between the sensor electrodes and the counter electrode. All of the foregoing apparatus are very complex in mechanical configuration and operation and typically require multiple, printed electrical leads. This leads to complicated operation in the devices which decreases any benefit obtained from large scale scanning systems.
Another approach to providing for the large scale scanning of a plurality of samples is disclosed in U.S. Pat. No. 7,074,318 which was filed by the inventors hereof, the disclosure of which is incorporated herein by reference. The prior art system described in the above-referenced patent describes a system for screening a plurality of materials disposed, in an array configuration, upon a common substrate. These samples are all in electrical communication with the substrate, which in turn is connected to an electrochemical analyzer. In a typical implementation, the substrate plate is covered with an electrically insulating layer having a plurality of openings formed therein, and the samples being tested are exposed in the openings. In this manner, the samples are all connected to the substrate, but are spaced from one another by the insulating, upper coating.
The system of the U.S. Pat. No. 7,074,318 patent further includes a large area counter electrode assembly which is separated from the substrate and associated array of test samples. This counter electrode assembly is in electrical communication with the analyzer. A relatively long, typically flexible, ionically conductive member, referred to as ionic conductive wire, is used to provide electrical and ionic conductivity between the counter electrode and selected members of the array. When such ionic conductivity is established, the selected member of the array and the counter electrode form an electrochemical cell, and the analyzer may be used to analyze the electrochemical properties of that resultant cell. By moving the ionically conductive wire from one member of the array to another, the entire array may be sequentially scanned. The ionic resistance of the ionically conductive wire is relatively high; therefore, only a very small current, typically less than 1 mA, can be measured by the apparatus of the prior art. This greatly restricts the utility of the system and the nature of the measurements which may be made thereby.
As will be apparent from the following, there is a need for a system which allows for the high speed, simple, and accurate measurement of electrochemical properties of a plurality of test samples.